Adamantane derivatives have been expected to be used as a raw material for producing a high-function material such as a highly heat resistance polymer material or an electronic material such as a semiconductor resist because they exhibit excellent heat resistance and transparency. Among others, dihalogenated adamantanes are important as raw materials for preparing a variety of adamantane derivatives having bifunctional groups.
A variety of halogenated adamantanes have been prepared from adamantane, for example, by reacting adamantane with a haloalkane in the presence of an aluminum halide [Synth. Commun., 19(9-10), 1697-1704 (1989)] or by reacting adamantane with a haloalkane in the presence of a cobalt salt [RU 2125551 (1999)]. These processes, however, generally provide a mixture of mono-, di-, and/or tri-halogenated adamantanes. Furthermore, such a mixture generally contains a monohalogenated adamantane as a main product, with a lower yield of a dihalogenated adamantane.
Tetrahedron Letters 31, 3191-3192 (1972) has disclosed a process for selectively preparing a dihalogenated adamantane, where adamantane is mixed and reacted with a halosulfonic acid at 20° C. In this synthetic method, the reaction, however, sharply proceeds during the initial stage. Thus, when using a sufficient amount of a halosulfonic acid in attempting to improve an yield, the reaction tends to excessively proceed, leading to formation of trihalogenated derivatives. The above preparation process is, therefore, improper with respect to an yield of a dihalogenated adamantane. For example, when adamantane and chlorosulfonic acid are charged in the molar ratio of 1:8 and reacted for about 10 hours, an yield of 1,3-dichloroadamantane is 80% or less as determined by gas chromatography.
For selectively preparing a dihalogenated adamantane, Zh. Org. Khim., 22 (3), 540-542 (1986) and Helv. Chim. Acta, 68 (5), 1196-1203 (1985) have used an iron halide. However, when preparing a dihalogenated adamantane using a metal compound, a dihalogenated adamantane prepared may be frequently contaminated with a metal. In an electronic device, contamination with a trace amount of a metal may be deleterious to its performance. A dihalogenated adamantane prepared according the process cannot be, therefore, used for manufacturing such an electronic device. Further purification of a dihalogenated adamantane contaminated with a metal is cumbersome, leading to increase in a cost.
The above preparation process may provide a dihalogenated adamantane in a relatively higher yield, but the dihalogenated adamantane thus prepared inevitably contains several percents of a monohalogenated adamantane, which is an intermediate. For providing the highly pure dihalogenated adamantane, separation of the monohalogenated adamantane is essential. These compounds, however, exhibit very similar chemical properties, and thus cannot be separated by a common and convenient method. They are, therefore, generally separated by chromatography. However, chromatographic separation can deal with a small amount in a single run and takes much time, leading to lower overall productivity. Thus, the procedure is not suitable for production in a large scale.